Chapter 6 - Clinical Corner

Eight children, all under the age of 9 years, are brought into the emergency room complaining of various degrees of diarrhea and vomiting. After initial examination it is learned that all of the children are from the same elementary school class and that the class was taken on a field trip to a nearby water park on the previous day.
A. What is the likely reason for their condition?
B. How would you confirm your suspicions for what the likely reason for their condition is?
C. What are the epidemiological possibilities?

Question A: Although the children may have become ill because of a shared snack, it is most likely that they became ill because of poor chlorination of the pool which resulted in the water becoming a reservoir for infection. The two most common pathogens that are leading candidates for the role of causative agent are norovirus and toxigenic E. coli as they both produce intestinal disease. Two other possible candidates are Giardia and Cryptosporidium which are most often seen in untreated and poorly-treated community water supplies. However, as the infection was restricted to the water park these two pathogens are unlikely causes.
Question B: The pathogen responsible would need to be determined in the laboratory. Diagnosis of E. coli is based on the isolation of the organism from clinical specimens in the microbiology laboratory. E. coli is a Gram-negative bacillus that grows well on commonly used media, it is lactose-fermenting and beta-hemolyic on blood agar, and appears as red stained colonies on MacConkey’s agar. Diagnostic methods for norovirus require detection of viral RNA or antigen as human noroviruses cannot be grown in culture. Most public health and clinical virology laboratories can test for norovirus using real-time reverse transcription-polymerase chain reaction (RT-PCR) assays. RT-PCR involves reverse transcription of the RNA template into complementary DNA (cDNA) using reverse transcriptase, followed by exponential amplification of the cDNA. These assays are currently the most sensitive method for detecting the virus.
Question C: To prevent further infections the water park should be closed and the water treated with antiseptics until the water tests negative for the pathogen. Thorough hand washing is also necessary for patients and all those taking care of them to prevent spread of the infection.

Shady Grove retirement village has experienced an outbreak of bacterial pneumonia. This is a common problem seen in nursing home facilities. Eighteen of the 50 residents of the facility have severe symptoms and must be sent to the hospital.
A. What are the possible reasons that only 18 of the 50 residents became ill?
B. How could the disease have spread?
C. Explain whether this is a common-source outbreak or a propagated epidemic.
D. What are the main concerns you would have for the residents sent to the hospital?

Question A: Most episodes of bacterial pneumonia are caused by aspiration of pharyngeal flora into the lung and by failure of host defense mechanisms to eliminate aspirated bacteria. Patients at a nursing home who have difficulty swallowing or are being fed through a tube and those with symptoms of dementia or chronic lung disease are most susceptible. Patients without debilitation of breathing problems tend to be resistant.
Question B: Medical devices such as nebulizers, bronchoscopes, and spirometers are potential reservoirs and vehicles for pneumonia pathogens. In a nursing home the patient might receive the organism from another patient or from contaminated reservoirs of aerosol-producing devices. Proper cleaning and sterilization or disinfection of reusable equipment would be part of a program to reduce transmission of the disease.
Question C: In a nursing home the patient might receive the organism from another patient or from contaminated reservoirs of aerosol-producing devices and the infection can be considered either a common-source outbreak or propagated epidemic depending on the mode of transmission. It is most likely to be a common-source outbreak arising from contact with contaminated substances. Amplification of the number of infected individuals through person-to-person contact would result in a propagated epidemic.
Common-source outbreaks are epidemics that most commonly occur when a water supply is contaminated with fecal matter or when food is improperly prepared. Although such outbreaks affect large numbers of people they quickly subside when the source of contamination has been identified and resolved. A propagated epidemic is one that results from amplification of the number of infected individuals as person-to-person contacts occur. Propagated epidemics stay in the population for long periods and are more difficult to deal with than common-source outbreaks.
Question D: Patients sent to the hospital might be in further danger of worsening their existing condition or contracting secondary infections. The stress of moving to the hospital may further aggravate their condition and hospitals are ready sources of antibiotic-resistant organisms. It may be possible not to send patients to hospital as treatments such as intravenous antibiotics and fluids can be delivered in many nursing homes.